Which cells make the myelin sheath around the axons of the nerves of the body? …
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
- Which cells make the myelin sheath around the axons of the nerves of the body?
- What are the nodes of Ranvier?
- Explain why an impulse travels faster in a myelinated fibre.
- Suppose that the myelin of a nerve is damaged. What do you expect for the speed of conduction? Give a reason.
Need a reminder? The key ideaShow
Neural tissue controls the responses of the body. The neuron is the unit of the nervous system. A neuron has a cell body (cyton) with the nucleus and Nissl granules, dendrites that bring impulses to the cell body, and an axon that carries impulses away. The axon ends in axon terminals. A myelinated axon has a myelin sheath with gaps called nodes of Ranvier. The impulse jumps from node to node, so a myelinated fibre conducts faster than an unmyelinated one. Neuroglia support and protect neurons and make up more than half the volume of neural tissue. The time taken by an impulse is the distance divided by the speed.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The Schwann cells.
Step 2. (b) Small gaps in the myelin sheath, between one stretch of the sheath and the next.
Step 3. (c) The impulse jumps from node to node, and does not travel along the whole membrane. This saves time.
Step 4. (d) The speed would fall, because the jumping between nodes would be lost. This is an inference from the mechanism.
Answer: (a) Schwann cells; (b) gaps in the sheath; (c) the impulse jumps from node to node; (d) slower conduction, as there are no nodes to jump between.
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